Pseudomonas toxin has been coupled to monoclonal antibodies to make immunotoxins. When coupled to an antibody to the T cell growth factor receptor to make anti TAC-PE, it kills leukemia cells that are TAC positive. When coupled to an antibody to the human transferrin receptor (anti-TFR-PE), it kills various tumor cell lines. Cell killing is related to the number of molecules bound and taken into cells. Adenovirus enters cells in the same vesicle as these immunotoxins. By lysing this vesicle, adenovirus efficiently releases the immunotoxins into the cytosol and selectively increases cell killing. The penton base of adenovirus is important for vesicle lysis.